1. Field of the Invention
This invention relates to powder coating materials and particularly to such materials prepared from ionic copolymers or copolymers or terpolymer base resin thereof and monobasic fatty acids or metallic salts of monobasic fatty acids.
2. Description of the Prior Art
Ionic copolymer coatings show good adhesion to many substrates, including glass. Such ionic copolymer coatings fused on glass bottles, such as nonreturnable beverage bottles, show initial adhesion to the glass which generally exceeds the ultimate tensile strength of the coatings. Due to absorption of water by the coating upon aging it has been found that the adhesion of the coating decreases. In fact, it may take as long as three weeks or more before a level of decreased adhesion is reached whereby the coating becomes peelable (ultimate tensile strength of the polymer exceeds the adhesion). Ionomeric copolymers also are notch sensitive materials. Therefore, cracks in the glass, when broken, propagate into the coating, greatly decreasing the fragment retaining ability of the plastic coating which is referred to as cullet retention. It is desirable to achieve controlled reduction in adhesion in a period of 24 to 48 hours or less and thereby obtain maximum cullet retention of the glass. Metallic salts of stearic and oleic acids are known release agent additives in polyolefin resins, e.g., for chill roll release in extrusion coating and for slip and anti-block in blown film. These additives are generally incorporated into the polymer by melt blending whereby the plastic pellets used to make coatings contain the additive dispersed or blended uniformly throughout the polymer.